Measurement of steep aspheric surfaces

Area of Science:

• Optical Engineering
• Metrology
• Surface Science

Background:

• Accurate measurement of aspheric surfaces is critical for advanced optical systems.
• High numerical aperture (NA) optics present unique metrology challenges due to steep slopes.
• Existing methods may lack the precision or adaptability for complex aspheric geometries.

Purpose of the Study:

• To develop and validate a precise method for measuring high NA aspheric surfaces.
• To assess the reproducibility of aspheric surface fabrication using a novel technique.
• To achieve measurement errors below 0.1 micrometers for convex and concave aspheres.

Main Methods:

• A two-step measurement process is employed.
• Step 1: Standard metrology to establish a reference surface.
• Step 2: Holographic comparison to evaluate fabrication reproducibility, accommodating slopes up to 1200 waves/rad.

Main Results:

• The holographic comparison method demonstrates high precision for aspheric surface measurement.
• The method successfully measures surfaces with high numerical apertures (NA < 0.95).
• Achieved measurement errors are consistently below 0.1 micrometers.

Conclusions:

• The described holographic method offers a robust solution for metrology of challenging aspheric optics.
• This technique enables reliable assessment of aspheric surface fabrication reproducibility.
• The high accuracy and precision are suitable for demanding optical manufacturing applications.